Whipstock assembly

ABSTRACT

The whipstock assembly comprises an assembly casing (9) with preformed windows connected to production casing (7); a landing tube (21) is located within assembly casing (9) for receiving whipstock shaft; a key is located within tube (21) for cooperation with J-slot on whipstock shaft. The whipstock consists of upper (49) and lower (55) portion which are fixed against relative rotation by splines. The assembly casing (9) with landing tube (21) is positioned in the borehole using a gyro survey tool for correct orientation of the windows. After a first side hole has been drilled, upper portion (49) is raised and rotated to place wedge surface (51) for drilling a second side hole. Tube (21) is initially closed by a cap containing a marking fluid; after the cap has been drilled out the marking fluid indicates the removal of the cap. In a second embodiment two vertically spaced side holes are drilled.

The present invention relates to an assembly for creating boreholebranches from a wellbore formed in an earth formation. More particularlythe invention relates to an assembly which allows wellbore tools, forexample drilling tools or production stimulation tools, to be directedselectively into different deviated borehole branches, and allowingcontrolled re-entry of the tools.

Whipstocks are commonly used in well drilling in order to deviate thewellbore from an essentially vertical course to a desired inclination.Such whipstocks include tapered sections of round, solid bar which areplaced in the wellbore at the desired depth and aligned in the desireddirection. They are typically anchored by a slip mechanism, and are usedto guide wellbore tools in a selected direction. Generally it isrequired to mill a window through the casing at the desired kick-offpoint to permit access to the rock formation around the casing. Whenonly one deviated borehole is drilled, the whipstock is sometimes leftin place to act as a guide for re-entry equipment. However, when two ormore directional boreholes are drilled from a wellbore it becomesnecessary to remove the whipstock from the well so that each of thedeviated boreholes can be produced. After removal of the whipstock,selective controlled re-entry into any of the deviated boreholes isdifficult and costly since a retrievable whipstock must be placed in theexact position required for re-entry.

It is an object of the invention to provide an assembly for creatingdeviated borehole branches from a wellbore, which assembly overcomes theaforesaid problems.

In accordance with the invention there is provided an assembly forcreating borehole branches from a wellbore formed in an earth formation,comprising a tool guide and positioning means defining a landingposition of the tool guide, the positioning means being connected to acasing of the wellbore, the tool guide being positionable at the landingposition thereof in at least two different orientations including afirst orientation whereby the tool guide guides a tool lowered throughthe casing in the direction of a first one of said borehole branches anda second orientation whereby the tool guide guides the tool in thedirection of a second one of said borehole branches.

The positioning means define an exact landing position for the toolguide, so that repeated positioning of the tool guide in the wellbore atthe same position can be achieved without difficulty. The differentorientations of the tool guide when in the landing position allow entryof wellbore tools in the different borehole branches. The invention canbe used on new wells drilled from surface, or on existing wells whichare to be extended.

To create borehole branches of different azimuth angles, suitably thetool guide in the first orientation thereof is oriented in a firstangular orientation about the wellbore axis, and the tool guide in thesecond orientation thereof is oriented in a second angular orientationabout the wellbore axis.

Such different angular orientations are suitably achieved if the toolguide includes an upper part and a lower part connectable to saidpositioning means, the upper part being orientable relative to the lowerpart in said angular orientations.

Preferably the upper part and the lower part are provided withco-operating splines to facilitate said angular orientations.

To avoid milling windows in the casing to drill the borehole branches,suitably the casing includes at least one window section, each windowsection being provided with at least one elongated opening, eachelongated opening being aligned with one of said borehole branches.

Preferably a removable liner is located inside each window section totemporarily close each opening of the window section during installationof the casing in the wellbore.

The invention will now be described by way of example in more detailwith reference to the accompanying drawings in which:

FIG. 1 shows schematically an embodiment of the assembly according tothe invention for drilling two opposite borehole branches from avertical wellbore formed in an earth formation;

FIG. 2 shows the assembly of FIG. 1 when installed in the wellbore;

FIG. 3 shows the assembly of FIG. 1 before positioning of a tool guidein the wellbore;

FIG. 4 shows the assembly of FIG. 1 after positioning of the tool guidein the wellbore;

FIG. 5 shows schematically an embodiment of the tool guide used in theassembly of FIGS. 1-4;

FIG. 6 shows schematically a wellbore casing for use in combination withanother embodiment of the assembly according to the invention;

FIG. 7 shows schematically a tool guide in a first mode for use with thewellbore casing of FIG. 6; and

FIG. 8 shows the tool guide in a second mode for use with the wellborecasing of FIG. 6.

For the purpose of clarity, in the Figures only reference numerals ofthe main components are indicated, whereby like reference numeralsrelate to like components.

Referring to FIGS. 1-4 there is shown a tubular wellbore casing 1 forinstallation in a wellbore 3 formed in an earth formation 5. Thewellbore casing 1 includes an upper part forming production casing 7 anda lower part forming assembly casing 9 extending to near the lower endof the wellbore 3. The assembly casing 9 consists of the followingsections in subsequent order in downward direction: a cementing andorienting section 11, a window section 13, a landing section 15, and acasing tail joint 17. The casing tail joint 17 is at its lower providedwith a float shoe (not shown) which prevents flow of fluid and debrisback into the wellbore casing 1. The various sections 7, 11, 13, 15, 17are interconnected by conventional casing connectors 18a, 18b, 18c, 18dor by other suitable means, and casing stabilisers 19a, 19b, 19c areprovided to the casing 1 at regular intervals to centralise the wellborecasing 1 in the wellbore 3.

The landing section 15 is provided with a concentric tube 21 fixed tothe inner wall of the landing section 15 by means of spacers 23 in amanner that an annular space 25 is formed between the tube 21 and theinner surface of the casing 1. The tube 21 is closed at its lower end bya bottom 27 fitted with a check valve (not shown) to allow pressureequalisation during cementing operations and to prevent fluid flow outof tube 21. The upper end of the tube 21 is temporarily closed by analuminium cap 29 which is to be drilled out when a retrievable whipstockdescribed hereinafter is to be installed in the landing section 15. Amarker of brightly coloured dye is located in the cap 29, which dye isreleased upon drilling through the top of the cap 29, circulated tosurface with the drilling fluid and made visible at surface to providean indication of the drilling status. The inner wall of the tube 21 isprovided with a key 31 to permit orientation of a retrievable whipstockdescribed hereinafter.

The window section 13 of the casing 1 is provided with two windows inthe form of elongated openings 33, 35 oppositely arranged and havingtheir longitudinal axes extending in the longitudinal direction of thewindow section 13, so that each opening 33, 35 describes theintersection of the casing 1 with one of the deviated borehole brancheswhich is to be drilled through said opening 33, 35. The profile of thewindows 33, 35 will therefore vary, depending on the outside diameter ofthe casing 1, the diameter of the deviated borehole branches, and thebuild radius of the bend from the wellbore to the deviated boreholebranches. The windows 33, 35 are aligned or set at a selected angle withrespect to the key 31 of tube 21. A fibreglass liner 37 is internallyprovided in the window section 13 to temporarily close the elongatedwindows 33, 35 during installation of the casing 1 in the wellbore 3,thereby preventing fluids from passing through the pre-cut windows 33,35.

The cementing and orienting section 11 of casing 1 is provided with atubular element 39 of smaller outer diameter than the inner diameter ofthe casing 1, which tubular element is internally provided with a key 41to form a landing profile for an azimuth landing tool (not shown). Thekey 41 is aligned, or set at a selected angle, with respect to the key31 in the casing landing section 15.

The tubular element 39 is fixed within the casing section 11 by means ofspacers 43. A one-way valve in the form of a float collar 45 is locatedbelow the tubular element 39, which float collar 45 allows cement toflow through the casing 1 in downward direction only. All components 39,41, 43, 45 located within casing section 11 are removable therefrom bythe action of a rotating drill bit (not shown) lowered into the casing1.

In FIG. 5 is shown a tool guide in the form of a retrievable whipstock47 having an outer diameter slightly smaller than the inner diameter ofcasing 1. The whipstock 47 consists of an upper part 49 having a taperedconcave surface 51 located aside the upper part 49 so as to matchdrilling tools when these are guided along the surface 51, a lower partin the form of a cylindrical stab element 53 of outer diameter slightlysmaller than the inner diameter of the tube 21, and a spacer part 55located between the upper part 49 and the stab element 53. The stabelement 53 is provided with a J-slot keyway 57 which matches key 31 oftube 21 when the stab element is stabbed into the tube 21 after removalof cap 29. The stab element 53 is provided with a guiding surface in theform of a mule shoe 58 to permit self-alignment of the J-slot keyway 57with key 31. The stab element 53 and the spacer part 55 are providedwith corresponding splines (not shown) allowing re-orientation of thespacer part 55 and the upper part 49 relative to the stab element 53 ina manner that the concave surface 51 can be oriented opposite eachelongated opening 33, 35 of the window section 13. Slots (not shown) areprovided into the upper part 49 of the whipstock 47 for attachment of aretrieving tool (not shown) thereto.

During normal use of the assembly according to the invention, theproduction casing 7 is set and cemented whereafter the wellbore 3 isdrilled or deepened to depth slightly below the desired kick-off point.The assembly casing 9 is then run into the wellbore 3. A gyro surveytool is run into the casing on wireline and landed in the orienting andcementing section 11, and the assembly casing 9 is rotated to orient thewindows 33, 35 with the desired azimuth of the deviated boreholes to bedrilled, whereafter the gyro survey tool is pulled from the wellbore 3.The assembly casing 9 is cemented in the wellbore 3 by pumping cement 59down the assembly casing 9 using a conventional wiper plug 60, wherebythe cement 59 flows through the annular space 25 formed between the tube21 and the inner surface of the casing 1. The cement 59 exits the casing1 at its lower end, and returns back up the annulus between the assemblycasing 9 and the wall of the wellbore 3 thereby surrounding the assemblycasing 9, including the window section 13.

As shown in FIG. 2, the wiper plug 60 lands in the cementing andorienting section 11 above the landing profile, and the float collar 45prevents back flow of the cement into the casing 1. After allowing thecement to gain compressive strength, a drill string with a drill bit ofdiameter equal to the inner diameter of the assembly casing 9 is runinto the assembly casing 9 and the wiper plug, the landing profile, andfloat collar are drilled out. Drilling continues through the windowsection 13 where the fibreglass liner 37 is drilled out, and through thelanding section 15 where the aluminium cap 29 is drilled out so thataccess to the interior of the tube 21 is achieved, reference being madeto FIG. 3. Cleaning fluid is then circulated through the drill stringand the casing 1 to clean the casing 1, whereafter the drill string isremoved from the wellbore 3.

Referring to FIGS. 4 and 5, the retrievable whipstock 47 is then runinto the casing 1 and landed in the landing section 15 whereby the stabelement 53 of the whipstock 47 is positioned in the tube 21 and the key31 matches with the J-slot keyway 57. In this position the concavesurface 51 of whipstock 47 is arranged opposite a first of the elongatedopenings 33, 35 of window section 13. Running of the whipstock 47 can bedone by wireline, by a drill string using a shear attachment to thedrill bit, or by using any other suitable means.

A conventional directional drilling assembly for drilling the buildsection of the borehole branches is then run into the wellbore 3 wherebythe drill bit of the assembly is guided along the concave surface 51 ofthe whipstock 47 and through a first one of the elongated openings 33,35. In this manner a first deviated borehole branch is drilled. Tore-orient the whipstock 47 in order to drill the second deviatedborehole branch, a suitable retrieving tool is latched into the slots inthe upper part 49 of the whipstock, and the upper part 49 and the spacerpart 55 of the whipstock 47 are pulled from the stab element 53 whichremains located in the tube 21. The upper part 49 and the spacer part 55are then re-oriented relative to the stab element 53 using the splinesso that the concave surface 51 of the whipstock 47 is located oppositethe second one of the elongated openings 33, 35 of window section 13.The second deviated borehole branch is then drilled whereby the drillbit is guided along the concave surface 51 of the whipstock 47 andthrough the second one of the elongated opening 33, 35.

Referring to FIG. 6 there is shown a part of a wellbore casing includinga casing assembly 70 having an upper window section 72, an intermediatecasing 70, a lower window section 74 and a landing section 76, whichsections are interconnected by casing connectors 78a, 78b. The landingsection 76 is at it lower end provided with a guide shoe 80 to guide thecasing during lowering thereof in the wellbore.

The landing section 76 is provided with a tube 82 concentricallyarranged within the landing section 76, which tube 82 is fixed withinthe landing section 76 at the lower end thereof. The upper end of thetube 82 is closed by an aluminium cap 84 which is to be drilled out whena retrievable whipstock described hereinafter is to be installed in thelanding section 76. The tube 82 is closed at its lower end and providedwith a check valve (not shown) to allow pressure equalisation duringcementing operations and to prevent fluid flow out of tube 82. The tube82 is internally provided with a gripping profile 88. Another tube 90communicates with the check valve 86 and extends along the casing tosurface.

The upper window section 72 is provided with an elongate window 92 andthe lower window section 74 is provided with an elongate window 94, bothwindows 92, 94 having their longitudinal axes aligned with thelongitudinal direction of the casing. In FIG. 6 the windows 92, 94 areshown aligned so that the borehole branches to be drilled through thewindows 92, 94 extend in the same direction. Alternatively each windowcan be oriented in any desired direction depending on the desireddirections of the borehole branches, for example the windows can beoriented in opposite directions or in mutually perpendicular directions.Internal guiding profiles (not shown) and alignment slots 96, 98 areprovided in the upper and lower window sections 72, 74 respectively. Theinternal guiding profiles serve to guide a key of a whipstock (describedhereinafter) into the slots 96, 98. The alignment slots 96, 98 arealigned with the respective windows 92, 94. A fibreglass liner (notshown) is internally provided in the window sections 72, 74 totemporarily close the windows 92, 94 during installing and cementing thecasing in the wellbore.

In FIG. 7 is shown a drillstring guide in the form of a retrievablewhipstock 100 having an outer diameter slightly smaller than the innerdiameter of casing. The whipstock 100 consists of an upper part 102having a tapered concave surface 104 so as to match drilling tools whenthese are guided therealong, a lower part in the form of a stab element106 of outer diameter corresponding to the inner diameter of the tube82, and a spacer part 108 in-between the upper part 102 and the stabelement 106. The upper part is provided with a spring-loaded key 109which during operation co-operates with slot 96 or slot 98. The spacerpart 108 is made up of a number of interconnected spacer bars 110 and aswivel 114 which allows the upper part 102 to swivel around thelongitudinal axis of the whipstock 100 relative to the stab element 106.The number of spacer bars 110, 112 is selected so that, when the stabelement 106 is located in tube 82, the key 109 is latched in slot 98 andthe concave surface 104 is located opposite the window 94. The stabelement 106 is provided with a gripping profile 116 corresponding to thegripping profile 88 of the tube 82, and a compression packer 118. Thelowermost spacer bar 110 is attached to the stab element 106 by areleasable connector (not shown). A longitudinal bore 120 extendsthrough the whipstock 100 to provide fluid communication between theinterior of the tube 82 when the stab element 106 is located therein,and the concave surface 104. The bore 120, which is internally providedwith a check valve 122, divides into two bores 124, 126 near the concavesurface 104.

During normal use of the assembly shown in FIGS. 6-8, the casingassembly casing 70 is run into the wellbore, oriented in the desireddirection and cemented in the wellbore. The cap 84 prevents cement fromentering the tube 82. After hardening of the cement, a drill string islowered into the casing assembly 70 to drill out cement present in thecasing assembly and to drill out the fibreglass liner. Drillingcontinues through the landing section 15 whereby the aluminium cap 84 isdrilled out so that access to the interior of the tube 82 is achieved.Cleaning fluid is then circulated through the tube 90 to clean theinterior of the tube 82 and the casing assembly 70.

The retrievable whipstock 100 is then run into the casing assembly 70and landed in the landing section 76 whereby the stab element 106 islatched into the tube 82 and the gripping profiles 88, 116 co-operate toretain the stab element 106 in the tube 82. The key 109 of the whipstock100 is guided along the guiding profile of window section 74 until thekey 109 latches into slot 98. During guiding of the key 109 along theguiding profile, the upper part 102 of the whipstock 100 is allowed torotate around its longitudinal axis by means of swivel 114. In the finalposition the concave surface 104 is arranged opposite the window 94. Afirst borehole branch is then drilled by drilling through the window 94,whereby the drill bit of the assembly is guided along the concavesurface 104 of the whipstock 100.

When drilling of a second borehole branch through the upper window 92 isdesired, a suitable retrieving tool is latched onto the whipstock 100whereafter the upper part 102 and the spacer part 108 are pulled fromthe stab element 106 which remains located in the tube 82. The upperpart 102 and the spacer part 108 are retrieved to surface, and one ormore spacer bars 110 are added to the spacer part 108, as shown in FIG.8. The number of spacer bars 110 is selected so that, when the stabelement 106 is located in tube 82, the key 109 is latched in slot 96 andthe concave surface 104 is located opposite the window 92. The upperpart 102 and spacer part 108 are lowered through the casing assembly 70and re-connected to the stab element 106 by means of the releasableconnector, whereby the key 109 is guided along the guiding profile ofwindow section 72 until the key 109 latches into slot 96. Again, theswivel 114 allows rotation of the upper part 102 relative to the stabelement 106 during guidance of the key 109 along the guiding profile. Inits final position the concave surface 104 is arranged opposite thewindow 92, whereafter drilling of the second borehole is started throughthe window 92.

When the whipstock 100 is installed, either with the concave surface 104opposite window 92 or opposite window 94, cleaning fluid can becirculated through the casing assembly 70 via tube 90 and bores 120,124, 126 of the whipstock. Check valves 86, 122 prevent undesired flowof drilling fluid through the bores 120, 124, 126 and the tube 90.

Optionally one or more compression packers 130 can be provided at thespacer bars 110 to prevent drilling fluid from flowing to the lower partof the casing assembly 70.

Instead of the arrangement of key and slots as shown in FIGS. 6-8, aJ-slot keyway at the stab element and a corresponding key provided atthe tube, or a J-slot keyway at the tube and a corresponding keyprovided at the stab element, can be applied. In such alternativearrangements there would be no need for a swivel at the whipstock. Theabsence of a key at the inner surface of the tube allows drillingthrough the tube whereby the bottom of the tube is drilled out, andsubsequent drilling through the bottom of the casing tail joint in orderto drill a lower borehole section either straight or inclined, in aconventional manner.

Access to either of the deviated borehole branches for future remedialwork can be accomplished by re-running the retrievable whipstock in thedesired position or orientation.

The entire assembly, including the retrievable whipstock, can beconstructed from non-magnetic materials to permit the use ofconventional magnetic directional survey instruments in the drillingassembly for the purpose of orienting the drilling assembly upon exitingthe windows for drilling the build sections. In the above describedembodiments the assembly has two windows for drilling of two boreholebranches. Alternatively the assembly can be provided with any suitablenumber of windows to drill a corresponding number of deviated boreholebranches.

Instead of the marker of brightly coloured dye, any suitable marker canbe provided which is released upon drilling therethrough and which formsa detectable part of the drilling fluid circulated to surface so as toprovide an indication of the status of drilling through the assembly.Furthermore, other parts of the assembly can in a similar manner beprovided with a marker, for example in the cementing and orientingsection, or in the window section.

We claim:
 1. Assembly for creating borehole branches from a wellboreformed in an earth formation, comprising a tool guide and positioningmeans defining a landing position of the tool guide, the positioningmeans being connected to a casing of the wellbore, the tool guide beingpositionable at the landing position thereof in at least two differentorientations including a first orientation whereby the tool guide guidesa tool lowered through the casing in the direction of a first one ofsaid borehole branches and a second orientation whereby the tool guideguides the tool in the direction of a second one of said boreholebranches;wherein said positioning means includes a tube arrangedsubstantially concentrically within the casing, and the tool guideincludes a stab element to be received in said tube when the tool guideis in the landing position, and the tube is provided with removablesealing means to seal the interior of the tube from the interior of thecasing during installation of the casing in the wellbore.
 2. Theassembly of claim 1, wherein the tool guide in the first orientationthereof is oriented in a first angular orientation about the wellboreaxis, and the tool guide in the second orientation thereof is orientedin a second angular orientation about the wellbore axis.
 3. The assemblyof claim 2, wherein the tool guide includes an upper part and a lowerpart connectable to said positioning means, the upper part beingorientable relative to the lower part in said angular orientations. 4.The assembly of claim 3, wherein the upper part and the lower part areprovided with co-operating splines to facilitate said angularorientations.
 5. The assembly of claim 3, wherein the tool guideincludes a swivel allowing rotation of the upper part of the tool guiderelative to the lower part thereof about the longitudinal axis of thetool guide.
 6. The assembly of claim 1, wherein said borehole branchesdeviate from the wellbore at different levels thereof, wherein the toolguide is operable in a first mode and a second mode in which the toolguide is longer than in the first mode, the difference in length of thetool guide in said two modes corresponding to the difference in levelsof the said borehole branches.
 7. The assembly of claim 6, wherein thetool guide includes a spacer part which comprises at least one spacerbar, the number of spacer bars being selected in accordance with thelength of the tool guide.
 8. The assembly of claim 1, wherein thesealing means forms a cap covering the upper end of the tube.
 9. Theassembly of claim 1, wherein said sealing means is removable from thetube by the action of a rotating drill bit lowered through the casing.10. The assembly of claim 9, wherein the tube is provided with markingmeans which is released upon drilling away the sealing means, themarking means flowing with the drilling fluid to the surface so as toprovide an indication of removal of the sealing means.
 11. The assemblyof claim 1, wherein an orientation keyway is provided at the innersurface of the tube, said keyway co-operating with an orientation keyprovided at the stab element so as to orient the tool guide when thetool guide is brought in the landing position.
 12. The assembly of claim1, wherein said tube is filled with a lubricant to promote stabbing ofthe stab element into the tube.
 13. The assembly of claim 1, wherein thecasing includes at least one window section, each window section beingprovided with at least one elongated opening, each elongated openingbeing aligned with one of said borehole branches.
 14. The assembly ofclaim 13, wherein a removable liner is located inside each windowsection to temporarily close each opening of the window section duringinstallation of the casing in the wellbore.
 15. The assembly of claim13, wherein the casing includes an orienting section provided with meansfor landing an azimuth survey tool therein, which tool has a selectedorientation relative to the elongated openings of the window sectionwhen the tool is landed in the orienting section.
 16. Assembly forcreating borehole branches from a wellbore formed in an earth formation,comprising a tool guide and positioning means defining a landingposition of the tool guide, the positioning means being connected to acasing of the wellbore, the tool guide being positionable at the landingposition thereof in at least two different orientations including afirst orientation whereby the tool guide guides a tool lowered throughthe casing in the direction of a first one of said borehole branches anda second orientation whereby the tool guide guides the tool in thedirection of a second one of said borehole branches and wherein the toolguide in the first orientation thereof is oriented in a first angularorientation about the wellbore axis, and the tool guide in the secondorientation thereof is oriented in a second angular orientation aboutthe wellbore axis, and the tool guide includes an upper part and a lowerpart connectable to said positioning means, the upper part beingorientable relative to the lower part in said angular orientations, andwherein the upper part and the lower part are provided with co-operatingsplines to facilitate said angular orientations.
 17. Assembly forcreating borehole branches from a wellbore formed in an earth formation,comprising a tool guide and positioning means defining a landingposition of the tool guide, the positioning means being connected to acasing of the wellbore, the tool guide being positionable at the landingposition thereof in at least two different orientations including afirst orientation whereby the tool guide guides a tool lowered throughthe casing in the direction of a first one of said borehole branches anda second orientation whereby the tool guide guides the tool in thedirection of a second one of said borehole branches, said boreholebranches deviating from the wellbore at different levels thereof,wherein the tool guide is operable in a first mode and a second mode inwhich the tool guide is longer than in the first mode, the difference inlength of the tool guide in said two modes corresponding to thedifference in levels of the said borehole branches.
 18. The assembly ofclaim 17 wherein the tool guide includes a spacer part which comprisesat least one spacer bar, the number of spacer bars being selected inaccordance with the length of the tool guide.